Marc Warren produced a stunning finish to his first round to set the clubhouse target on day one of the Open de España.
The Scot birdied five of his last seven holes to sign for a 66 and move to six under, one shot clear of World Number Four Jon Rahm and another local favourite in amateur Victor Pastor.
The Spaniard is ranked 113th in the World Amateur Golf Ranking and is aiming to become the first amateur winner on the European Tour since Shane Lowry at the 2009 3 Irish Open.
Frenchman Julien Guerrier, Australian Jason Norris, Austrian Matthias Schwab, England's Jonathan Thomson and South African Erik van Rooyen were also at five under on a congested leaderboard at Centro Nacional de Golf.
Defending champion Andrew Johnston, Dane Thorbjørn Olesen, local favourite Pedro Oriol and South African Richard Sterne were then at four under.
Warren sandwiched a bogey on the fourth with birdies on the second and fifth to turn in 35 but really came to life on the back nine. The three-time European Tour winner birdied the 12th and 13th, followed that with two pars, but then closed with three further gains to jump out into the lead.
Pastor made a flying start with an eagle on the tenth and added further gains on the 13th, 18th and first as he surged up the leaderboard. A bogey on the fourth threatened to stall his momentum but birdies on the seventh and eighth gave him a share of the lead before he bogeyed the ninth.
Norris had been the first man to set the target at five under, the Fiji International champion carding birdies on the first, fifth, 13th, 15th and last but Rahm soon joined him.
The home hero birdied the 13th and while he gave the shot back on the next, an eagle on the 18th saw him turn in 34.
He put his tee-shot close on the third for another gain, made a good par save from a cart path on the fourth and a beautiful chip on the par five fifth helped him into a share of the lead. A drive to the greenside rough on the par four seventh then allowed him pitch to close range and make another birdie.
Qualifying School graduate Thomson joined Rahm in eagling the 18th - his last - to join the group at five under. The big Englishman had earlier made birdies on the second, seventh, 13th and 14th, and a bogey on the ninth.
Schwab also came through Q School and he had birdies on the first, third, eighth, 11th, 16th and 18th to go with a bogey on the 14th.
Van Rooyen already has two top tens this year after making the step from the Challenge Tour and he had a roller coaster of a round in Madrid. Eagles on the 13th and first had helped him to six under but he bogeyed the third and fourth before picking the shots back up on the next two. A bogey on the eighth then dropped him out of the lead again.
Guerrier is another Challenge Tour graduate and he made eight birdies and a single bogey to lead on his own before surrendering a double on the eighth.
There is rarely a dull moment with Johnston and he once again entertained the crowds with a 68 containing seven birdies and three bogeys alongside Rahm.
Olesen was bogey-free in his round, making birdies on the 11tth, 12th, 18th and first, while Sterne also kept blue off the card with gains on the second, ninth, tenth and 16th.
Oriol had a single bogey on the third to go with gains on the 16th, 18th, first, second and sixth.
There was a group of nine players three shots off the lead including local favourite Adrian Otaegui, Hero Indian Open champion Matt Wallace and four-time winner Matteo Manassero.